<!DOCTYPE html>
<html lang="zh-CN">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>登录</title>
    <style>
        body{font-family:Arial,sans-serif;margin:0;padding:20px;display:flex;justify-content:center;align-items:center;min-height:100vh;background:#f5f5f5}
        .login-box{background:white;padding:20px;border-radius:5px;box-shadow:0 2px 10px rgba(0,0,0,0.1);width:300px}
        input{width:100%;padding:10px;margin:8px 0;border:1px solid #ddd;border-radius:4px;box-sizing:border-box}
        button{width:100%;padding:10px;background:#007bff;color:white;border:none;border-radius:4px;cursor:pointer}
    </style>
</head>
<body>
    <div class="login-box">
        <h2>登录</h2>
        <input type="text" placeholder="用户名" id="username">
        <input type="password" placeholder="密码" id="password">
        <button onclick="alert(document.getElementById('username').value?'登录成功':'请输入用户名')">登录</button>
    </div>
</body>
</html>